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Since light is massless it does not interact with particles unless that specific wavelength is on the emission and absorption spectrum.

The emission and absorption spectrum of an atom indicates the wavelengths of the photons which the atom can absorb, and the rest of the wavelengths of light just pass through the atom unimpacted.

This leads me to my question of why light would pass through, let's say a block of coal, made entirely of carbon atoms. Having a very limited emission and absorption spectrum, it would not be able to absorb all the wavelengths of light, meaning that a lot of the light shined on it should just pass through it Now, this is obviously not the case as a block of carbon atoms (coal) has a clear shadow and thus stops most of, if not all the (at least all the visible) light shined on it. Why does this happen? I would assume it has something to do with light behaving as both a particle and a wave and is reflected off of the surface of the object. But this leads to different questions such as: How large does the object have to be for this to happen? Does it only happen when there are multiple photons?

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  • $\begingroup$ Does this answer your question? Why aren't all objects transparent? $\endgroup$ Commented Apr 5, 2022 at 10:09
  • $\begingroup$ I get the fact that some wavelengths are absorbed and reemitted, while others simply pass through, but my question is why the photons behave differently when there are only a few particles, as opposed to when there are a lot. Fx if the light hits one carbon atom it while in most cases pass through without interacting, but when there are a lot of atoms (a block of coal) this no longer applies. $\endgroup$ Commented Apr 5, 2022 at 11:08

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